The invention relates to color luster pigments based on lamellar substrates coated with a metal oxide layer, in particular mica or mica coated with metal oxides, the metal oxide layer containing both titanium and iron.
Mica flake pigments containing iron are known and have also been used successfully for many years. This term describes both pigments in which iron oxide is precipitated, together with another metal oxide, in particular titanium dioxide, onto the mica platelet, and pigments in which the precipitations are carried out successively.
It is described in U.S. Pat. No. 3,087,828 that golden pigments which assume a reddish color shade on being calcined are obtained by depositing an Fe.sub.2 O.sub.3 layer onto a TiO.sub.2 layer. Pigments which contain, on mica, first a mixed layer of titanium oxide and iron oxide and above that a top layer of titanium dioxide and/or zirconium dioxide are described in German Patent No. 1,959,998.
German Patent No. 2,244,298 describes a process for the preparation of golden pearly luster pigments in which a mica pigment coated with TiO.sub.2 and/or ZrO.sub.2 is first coated with iron(II) hydroxide, and the latter is then oxidized to Fe.sub.2 O.sub.3.
Finally, mica pigments which carry a thick layer of Fe.sub.2 O.sub.3 on a very thin layer of TiO.sub.2 or Al.sub.2 O.sub.3 are described in German Offenlegungsschrift No. 2,723,871.
It has also already been suggested in German Patent No. 2,522,572 to provide mica pigments which have been coated with TiO.sub.2 in rutile form with an additional top layer composed of coloring metal oxides, Fe.sub.2 O.sub.3 also being mentioned. In fact, coatings of this type have also been carried out using relatively small amounts of iron oxide.
Advantageous pigments containing iron, in which the iron oxide is present in specific defined crystal modifications, are described in German Offenlegungsschrift No. 2,313,331.
In the process of German Offenlegungsschrift No. 3,528,256, mica pigments coated with titanium dioxide in rutile form are coated with a relatively large amount of iron oxide, so that a three-layer structure of rutile, pseudobrookite and iron oxide is formed, as can be demonstrated by X-ray structural analysis.
The golden color luster pigments based on mica coated with metal oxide hitherto known have an inadequate resistance to chemicals and heat in vitreous enamels and glazes or are unsuitable for use in cosmetics owing to the addition of toxic heavy metals.